The present invention relates to a sealing arrangement for a swivel comprising inner and outer mutually rotatable swivel members, wherein the swivel members have respective inner fluid paths communicating with each other through one or more associated annular spaces at the interface between the swivel members, the annular spaces being mutually sealed by means of sealing means.
Many different embodiments of swivel structures of the above mentioned type are in use within the industry. Within the offshore industry, swivel devices are used for example to allow of transfer of hydrocarbons (oil and gas) or another process fluid through coupling members which rotate or are to be rotatable in relation to each other, for example between a marine riser which is connected to a floating loading buoy, and a tube system on a tanker which is connected to the buoy and is to be rotatable about the buoy under the influence of wind, waves and water currents.
In different fields of use it may be of interest to use swivel devices which are constructed in such a manner that the inner and outer swivel members in a simple manner can be disconnected from each other, and wherein a swivel member later can be connected to a cooperating swivel member in another swivel device of the topical type, to form an operative swivel unit. It will here be of essential importance that the swivel members can be disconnected from or connected to each other in a simple, quick and safe manner, at the same time as an efficient and safe sealing between the swivel members is achieved.
Thus, it is an object of the invention to provide a sealing arrangement for a swivel of the topical type, which enables a quick and safe interconnection of the swivel members, and simultaneously an efficient and safe sealing between the annular spaces of the swivel members.
A simultaneous object of the invention is to provide such a sealing arrangement which results in that cooperating swivel members can be interconnected in a simple and quick manner in spite of relatively large tolerance deviations or center displacements between the swivel members, and with a minimal risk for damaging the swivel members.
A further object is to provide a sealing arrangement giving the possibility for a simple monitoring of static as well as dynamic seals, a barrier liquid having a higher pressure than the ambient pressure being used.
For the achievement of the above-mentioned object there is provided a sealing arrangement for a swivel of the introductorily stated type which, according to the invention, is characterized in that a first one of the swivel members on each side of the annular space or spaces is provided with a peripheral groove receiving a radially displaceable ring element which is provided with sealing means arranged for static sealing against the other swivel member and for dynamic sealing between the ring element and the side walls of the peripheral groove, so that the first swivel member apart from the ring elements is rotatable in relation to the other swivel member.
By means of the stated ring element structure there is achieved that the ring elements of the swivel center themselves between the swivel members within relatively large tolerances. This is achieved in that the ring elements are able to float freely in the radial direction and thus will absorb possible center deviations or center displacements between the swivel members.
An advantageous embodiment of the invention is characterized in that the sealing means are arranged to be operated hydraulically by means of barrier liquid having a higher pressure than that of the fluid against which it is to be sealed, the first swivel member being provided with a supply channel for the barrier liquid. By using a barrier liquid having a higher pressure than the ambient pressure, there is obtained a controlled leakage path in the direction from the barrier liquid to the topical process fluid, i.e. from a clean to a xe2x80x9cdirtyxe2x80x9d medium. The barrier liquid suitably may be a hydraulic oil which then simultaneously has a lubricating effect, and the sealing surfaces may be protected by allowing very small quantities of clean barrier fluid to leak out into xe2x80x9cthe processxe2x80x9d. By controlling the volume of barrier liquid over time, one will obtain an early warning about a possible leakage or other changes in the system.